5,482 research outputs found
Relationship Between the Foveal Avascular Zone and Foveal Pit Morphology
Purpose.To assess the relationship between foveal pit morphology and size of the foveal avascular zone (FAZ).
Methods. Forty-two subjects were recruited. Volumetric images of the macula were obtained using spectral domain optical coherence tomography. Images of the FAZ were obtained using either a modified fundus camera or an adaptive optics scanning light ophthalmoscope. Foveal pit metrics (depth, diameter, slope, volume, and area) were automatically extracted from retinal thickness data, whereas the FAZ was manually segmented by two observers to extract estimates of FAZ diameter and area.
Results. Consistent with previous reports, the authors observed significant variation in foveal pit morphology. The average foveal pit volume was 0.081 mm3 (range, 0.022 to 0.190 mm3). The size of the FAZ was also highly variable between persons, with FAZ area ranging from 0.05 to 1.05 mm2 and FAZ diameter ranging from 0.20 to 1.08 mm. FAZ area was significantly correlated with foveal pit area, depth, and volume; deeper and broader foveal pits were associated with larger FAZs.
Conclusions. Although these results are consistent with predictions from existing models of foveal development, more work is needed to confirm the developmental link between the size of the FAZ and the degree of foveal pit excavation. In addition, more work is needed to understand the relationship between these and other anatomic features of the human foveal region, including peak cone density, rod-free zone diameter, and Henle fiber layer
Understanding Pound-Drever-Hall locking using voltage controlled radio-frequency oscillators: An undergraduate experiment
We have developed a senior undergraduate experiment that illustrates
frequency stabilization techniques using radio-frequency electronics. The
primary objective is to frequency stabilize a voltage controlled oscillator to
a cavity resonance at 800 MHz using the Pound-Drever-Hall method. This
technique is commonly applied to stabilize lasers at optical frequencies. By
using only radio-frequency equipment it is possible to systematically study
aspects of the technique more thoroughly, inexpensively, and free from eye
hazards. Students also learn about modular radio-frequency electronics and
basic feedback control loops. By varying the temperature of the resonator,
students can determine the thermal expansion coefficients of copper, aluminum,
and super invar.Comment: 9 pages, 10 figure
The Higgs System in and Beyond the Standard Model
After the discovery of the Higgs boson particle on the 4th of July of 2012 at
the Large Hadron Collider, sited at the european CERN laboratory, we are
entering in a fascinating period for Particle Physics where both theorists and
experimentalists are devoted to fully understand the features of this new
particle and the possible consequences for High Energy Physics of the Higgs
system both within and beyond the Standard Model of fundamental particle
interactions. This paper is a summary of the lectures given at the third IDPASC
school (Santiago de Compostela, Feb. 2013, Spain) addressed to PhD students,
and contains a short introduction to the main basic aspects of the Higgs boson
particle in and beyond the Standard Model.Comment: 62 pages, 31 figures, Lectures of the IDPASC School at Santiago de
Compostela, Spain, February 201
Correlations of the elements of the neutrino mass matrix
Assuming Majorana nature of neutrinos, we re-investigate, in the light of the
recent measurement of the reactor mixing angle, the allowed ranges for the
absolute values of the elements of the neutrino mass matrix in the basis where
the charged-lepton mass matrix is diagonal. Apart from the derivation of upper
and lower bounds on the values of the matrix elements, we also study their
correlations. Moreover, we analyse the sensitivity of bounds and correlations
to the global fit results of the neutrino oscillation parameters which are
available in the literature.Comment: 37 pages, 146 figures, minor corrections, 17 additional figures,
version for publication in JHE
Comparison of nursing home residents admitted from home or hospital.
A growing elderly population coupled with a reduction in hospital long term care has led to an increase in the independent nursing home sector. This is an expensive resource. Proper placement is therefore essential to ensure its efficient use. Prior to the introduction of care management there was no standard assessment procedure for admission to nursing home care from different sources. A nursing home population (n = 624) in North and West Belfast was studied and mental scores, levels of disability, and the source of admission to the nursing home recorded. Residents admitted from geriatric medical units (n = 132) were compared with those from general medical and surgical wards (n = 168) and those from home (n = 243). Residents who were admitted from a geriatric unit were the most disabled, those admitted from home were the least and those from general wards had intermediate levels of disability (p < 0.005). This is likely to be the result of different assessment procedures for prospective nursing home residents. With the introduction of care management, it is hoped that standardised assessment will follow. The roles of different medical specialists in this process is not yet clear. Further study is needed to assess the appropriateness of placement in nursing homes under care management
Activating RNAs associate with Mediator to enhance chromatin architecture and transcription
Recent advances in genomic research have revealed the existence of a large number of transcripts devoid of protein-coding potential in multiple organisms. Although the functional role for long non-coding RNAs (lncRNAs) has been best defined in epigenetic phenomena such as X-chromosome inactivation and imprinting, different classes of lncRNAs may have varied biological functions. We and others have identified a class of lncRNAs, termed ncRNA-activating (ncRNA-a), that function to activate their neighbouring genes using a cis-mediated mechanism. To define the precise mode by which such enhancer-like RNAs function, we depleted factors with known roles in transcriptional activation and assessed their role in RNA-dependent activation. Here we report that depletion of the components of the co-activator complex, Mediator, specifically and potently diminished the ncRNA-induced activation of transcription in a heterologous reporter assay using human HEK293 cells. In vivo, Mediator is recruited to ncRNA-a target genes and regulates their expression. We show that ncRNA-a interact with Mediator to regulate its chromatin localization and kinase activity towards histone H3 serine 10. The Mediator complex harbouring disease- displays diminished ability to associate with activating ncRNAs. Chromosome conformation capture confirmed the presence of DNA looping between the ncRNA-a loci and its targets. Importantly, depletion of Mediator subunits or ncRNA-a reduced the chromatin looping between the two loci. Our results identify the human Mediator complex as the transducer of activating ncRNAs and highlight the importance of Mediator and activating ncRNA association in human disease
Origins of Mass
Newtonian mechanics posited mass as a primary quality of matter, incapable of
further elucidation. We now see Newtonian mass as an emergent property. Most of
the mass of standard matter, by far, arises dynamically, from back-reaction of
the color gluon fields of quantum chromodynamics (QCD). The equations for
massless particles support extra symmetries - specifically scale, chiral, and
gauge symmetries. The consistency of the standard model relies on a high degree
of underlying gauge and chiral symmetry, so the observed non-zero masses of
many elementary particles ( and bosons, quarks, and leptons) requires
spontaneous symmetry breaking. Superconductivity is a prototype for spontaneous
symmetry breaking and for mass-generation, since photons acquire mass inside
superconductors. A conceptually similar but more intricate form of
all-pervasive (i.e. cosmic) superconductivity, in the context of the
electroweak standard model, gives us a successful, economical account of
and boson masses. It also allows a phenomenologically successful, though
profligate, accommodation of quark and lepton masses. The new cosmic
superconductivity, when implemented in a straightforward, minimal way, suggests
the existence of a remarkable new particle, the so-called Higgs particle. The
mass of the Higgs particle itself is not explained in the theory, but appears
as a free parameter. Earlier results suggested, and recent observations at the
Large Hadron Collider (LHC) may indicate, the actual existence of the Higgs
particle, with mass GeV. In addition to consolidating our
understanding of the origin of mass, a Higgs particle with
GeV could provide an important clue to the future, as it is consistent with
expectations from supersymmetry.Comment: Invited review for the Central European Journal of Physics. This is
the supplement to my 2011 Solvay Conference talk promised there. It is
adapted from an invited talk given at the Atlanta APS meeting, April 2012. 33
pages, 6 figures. v2: Added update section bringing in the CERN discovery
announcemen
Behavior of multitemporal and multisensor passive microwave indices in Southern Hemisphere ecosystems
©2014. American Geophysical Union. All Rights Reserved. This study focused on the time series analysis of passive microwave and optical satellite data collected from six Southern Hemisphere ecosystems in Australia and Argentina. The selected ecosystems represent a wide range of land cover types, including deciduous open forest, temperate forest, tropical and semiarid savannas, and grasslands. We used two microwave indices, the frequency index (FI) and polarization index (PI), to assess the relative contributions of soil and vegetation properties (moisture and structure) to the observations. Optical-based satellite vegetation products from the Moderate Resolution Imaging Spectroradiometer were also included to aid in the analysis. We studied the X and Ka bands of the Advanced Microwave Scanning Radiometer-EOS and Wind Satellite, resulting in up to four observations per day (1:30, 6:00, 13:30, and 18:00-h). Both the seasonal and hourly variations of each of the indices were examined. Environmental drivers (precipitation and temperature) and eddy covariance measurements (gross ecosystem productivity and latent energy) were also analyzed. It was found that in moderately dense forests, FI was dependent on canopy properties (leaf area index and vegetation moisture). In tropical woody savannas, a significant regression (R2) was found between FI and PI with precipitation (R2->-0.5) and soil moisture (R2->-0.6). In the areas of semiarid savanna and grassland ecosystems, FI variations found to be significantly related to soil moisture (R2->-0.7) and evapotranspiration (R2->-0.5), while PI varied with vegetation phenology. Significant differences (p-<-0.01) were found among FI values calculated at the four local times. Key Points Passive microwave indices can be used to estimate vegetation moisture Microwave observations were supported by flux data Passive microwave indices could be used to estimate evapotranspiratio
Scaling of the 3P0 strength in heavy meson strong decays
The phenomenological 3P0 decay model has been extensively applied to
calculate meson strong decays. The strength \gamma\ of the decay interaction is
regarded as a free flavor independent constant and is fitted to the data. We
calculate through the 3P0 model the total strong decay widths of the mesons
which belong to charmed, charmed-strange, hidden charm and hidden bottom
sectors. The wave function of the mesons involved in the strong decays are
given by a constituent quark model that describes well the meson phenomenology
from the light to the heavy quark sector. A global fit of the experimental data
shows that, contrarily to the usual wisdom, the \gamma\ depends on the reduced
mass of the quark-antiquark pair in the decaying meson. With this
scale-dependent strength \gamma, we are able to predict the decay width of
orbitally excited B mesons not included in the fit.Comment: 7 pages, 5 tables, 2 figure
- …